OC之字符串及其操作函数

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一:字符串创建

1.普通创建:NSString *str = [[NSString alloc] initWithFormat:@"******%d普通-字符%d",4,5];
2.便利构造器:NSString *str2 = [NSString stringWithFormat:@"便利构造器"];
3.字面量形式(语法糖):NSString *str1 = @"我是字面量形式";(只能给不可变的NSString)

二:操作函数

1.判断字符串是否以某字符串开头或者结束

    NSString *string = @"aaaabcdef";
    BOOL l = [string hasPrefix:@"aba"];
    BOOL l1 = [string hasSuffix:@"def"];

2.字符串的大小写转换

    NSString *str = @"slkKKKFFFdjkd";
    subString = [str uppercaseString];//全大写
    subString = [str lowercaseString];//全小写
    subString = [str capitalizedString];//只首字母大写
    NSLog(@"%@",subString);

3.字符串截取

    3.1从某个位置开始截取
    NSString *subString = [string substringFromIndex:3];
    3.2截取到某个位置
    subString = [string substringToIndex:4];
    3.3NSRange范围截取
    NSRange range = NSMakeRange(3, 4);
    subString = [string substringWithRange:range];
    NSLog(@"%@",subString);

4字符串拼接

NSString *string = @"gold";
subString = [string1 stringByAppendingString:@".png"];

5字符串比较

    NSString *s1 = @"abc";
    NSString *s2 = @"cba";
    if(NSOrderedAscending == [s1 compare:s2]){
        NSLog(@"s1 < s2");
    }else if (NSOrderedDescending == [s1 compare:s2])
    {
        NSLog(@"s1 > s2");
    }else{
        NSLog(@"s1 = s2");
    }
注:compare返回值类型为一个枚举值:typedef NS_ENUM(NSInteger, NSComparisonResult)
{NSOrderedAscending = -1L, NSOrderedSame, NSOrderedDescending};

    BOOL equ = [s1 isEqualToString:s2];(这很好啊)
    NSLog(@"%d",equ);

6.字符串的替换

    NSString *string2 = @"lanoukejiyouxiangongsi";
    subString = [string2 stringByReplacingOccurrencesOfString:@"youxiangongsi" withString:@"yanfa21"];
    NSLog(@"%@",subString);

NSMutableString可变字符串(感觉不常用)

    NSMutableString *mtStr = [NSMutableString stringWithFormat:@"askdj"];
    拼接字符串(可变的没有返回值,直接改变自身)
    [mtStr appendFormat:@"******"];
    NSLog(@"%@",mtStr);
    插入字符串
    [mtStr insertString:@"uuuuu" atIndex:3];
    NSLog(@"%@",mtStr);
    删除字符串
    NSRange range1 = NSMakeRange(3, 5);
    [mtStr deleteCharactersInRange:range1];
    NSLog(@"%@",mtStr);
/*
     给定一个图片文件名，判断字符串中是否以“png”结尾，如果是就替换成“jpg”，如果不是，就拼接”.jpg”。
*/
    NSMutableString *picture = [NSMutableString stringWithFormat:@"dpng"];
    NSUInteger len = [picture length];
    NSRange rangep = NSMakeRange(len - 3, 3);
    if ( [picture hasSuffix:@"png"]) {
        //替换
        [picture replaceCharactersInRange:rangep withString:@"jpg"];
    }else{
        //拼接
        [picture appendFormat:@".jpg"];
    }
    NSLog(@"%@",picture);

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